Dynamically inserted StyleSheet shouldn't block loading.

third_party/WebKit/Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 707 matching lines @@
         LocalFrame* frame = loadingFrame();
         if (!m_owner->media().isEmpty() && frame && frame->document()) {
             RefPtr<ComputedStyle> documentStyle = StyleResolver::styleForDocument(*frame->document());
             RefPtrWillBeRawPtr<MediaQuerySet> media = MediaQuerySet::create(m_owner->media());
             MediaQueryEvaluator evaluator(frame);
             mediaQueryMatches = evaluator.eval(media.get());
         }
 
         // Don't hold up layout tree construction and script execution on stylesheets
         // that are not needed for the layout at the moment.
-        bool blocking = mediaQueryMatches && !m_owner->isAlternate();
+        bool blocking = mediaQueryMatches && !m_owner->isAlternate() && m_owner->isCreatedByParser();
         addPendingSheet(blocking ? Blocking : NonBlocking);
 
         // Load stylesheets that are not needed for the layout immediately with low priority.
         FetchRequest request = builder.build(blocking);
         CrossOriginAttributeValue crossOrigin = crossOriginAttributeValue(m_owner->fastGetAttribute(HTMLNames::crossoriginAttr));
         if (crossOrigin != CrossOriginAttributeNotSet) {
             request.setCrossOriginAccessControl(document().securityOrigin(), crossOrigin);
             setFetchFollowingCORS();
         }
         setResource(CSSStyleSheetResource::fetch(request, document().fetcher()));
@@ skipping 28 matching lines @@
 }
 
 DEFINE_TRACE(LinkStyle)
 {
     visitor->trace(m_sheet);
     LinkResource::trace(visitor);
     ResourceOwner<StyleSheetResource>::trace(visitor);
 }
 
 } // namespace blink